The invention relates to heat-sealable barrier laminates for the containment of essential oils and the prevention of loss of vitamin C in paperboard cartons, as well as to a process for making such laminates. More particularly, this invention relates to barrier laminates which are comprised of an improved heat-sealable non-foil composite structure which retains the vitamin C in juice at nutritional-claims levels throughout the normal expected shelf life when the carton/package is made as well as improving the retention of citrus juice flavor oils therein.
Heat-sealable low-density polyethylenes are well known to be components of current paperboard citrus juice cartons which provide little barrier to absorption and/or transmission of citrus juice essential flavor/aroma oils. Additionally, it is well known that impermeable materials such as aluminum foil, polar materials such as: polyamides, polyethylene terephthalates, polyvinylidene chlorides, polyvinyl chlorides, etc., and highly crystalline non-polar materials such as high-density polyethylene and polypropylene provide varying degrees of barrier to the absorption and/or transmission of non-polar citrus juice flavor oils such as d-Limonene, et al. However, these materials require a thick liquid contact low density polyethylene layer for heat sealability as well as an expensive tie layer to provide consistent adhesion between the LDPE and the barrier material. The thick LDPE liquid contact layer (1.5 mil) generally required in such cartons also absorbs citrus flavor/aroma oils, with resultant deleterious effects on product quality.
The existing commercial structure for a paperboard carton for juice and similar products has utilized an easily heat-sealable barrier laminate composed of paperboard sandwiched between two layers of low density polyethylene (LDPE). The LDPE is an inexpensive heat-sealable moisture barrier. The conventional structure falters in that the thick LDPE layer absorbs the essential oils of the juice after short periods of time causing integrity decay of heat seals, stress cracking of the layer and allows transmission of the essential oils into the paperboard and to the atmosphere. Additionally, the conventional structure provides virtually no barrier resistance to oxygen causing the juice to lose vitamin C in large amounts.
One other conventional structure adds two additional layers to the structure identified above, namely a foil layer and an additional LDPE layer. The expensive foil layer increases barrier resistance to the flow of oxygen, while the additional LDPE allows for ultimate heat-sealability of the laminate. The improved conventional structure has poor barrier properties relating to the absorption of essential oils and aromas, since the interior contacting layer is still a thick layer of LDPE.
The object of the present invention is to produce an improved juice packaging heat-sealable laminate material for a juice carton which does not transmit flavor/odor ingredients of citrus and other juices and exhibits an improved cost-to-performance ratio relative to foil-lined cartons.